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However, there is conflict too. WiMAX makes redundant the efforts of Wi-Fi specialists to extend the reach of their favourite technology and also places 802.11 into a far smaller role than its supporters have carved out for it, often unrealistically. This is the opportunity for wireless technologies finally to grow up and offer the speed, multimedia support and ubiquity that Wi-Fi can never deliver.
The newer standard holds all the real power. By providing a backbone for hotspots, based on standards rather than the various proprietary WLAN expansion technologies out there, it makes the idea of a ubiquitous wireless network to rival cellular far more realistic than it ever was with Wi-Fi alone, despite the claims of the enthusiasts. The equipment makers are eyeing it keenly - amid all the doubts about the sustainability of the hotspot boom, anything that offers them a new product line and helps to preserve the interest in Wi-Fi is to be welcomed. 802.16 is a highly complex standard which contains from
day one many of the features that are being retrofitted, with various degrees of clumsiness and baggage, into Wi-Fi, which was originally conceived as being very simple and is now taking on the burden of responsibility beyond its technological reach.
The 802.16-2004 standard specifies networks for the current fixed access market segment. The 802.16e amendment and the soon to be approved 802.16f and 802.16g task groups will amend the base specification to enable not just fixed, but also portable and mobile operations in frequency bands below 6 GHz.
802.16 is optimized to deliver high, bursty data rates to subscriber stations, but the sophisticated MAC architecture can simultaneously support real-time multimedia and isochronous applications such as VoIP as well. This means that IEEE 802.16 is uniquely positioned to extend broadband wireless beyond the limits of today’s Wi-Fi systems, both in distance and in the ability to support applications requiring advanced QoS such as VoIP, streaming video and online gaming.
WiMAX has various features that make it suitable for the longer term, although some like QoS may be incorporated into 802.11, which has failed to come up with specifications of its own in this area with any credibility. The 802.16a specification uses various PHY variants, but the dominant one is a 256-point orthogonal frequency division multiplexed (OFDM) carrier technology, giving it greater range than WLANs, which are based on 64-point OFDM. Another key difference of 802.16 is its use of time slots, allowing greater spectral efficiency for QoS capabilities.
Unlike the horror show that Wi-Fi went through with security, 802.16d WiMAX will use Triple Data Encryption Standard and Advanced Encryption Standard from its inception, a requirement for vendors doing business with many government organizations.
Systems based on the mobile version of the standard, which should ship towards the end of next year, will be able to achieve long distance wireless networking and will have far greater potential than Wi-Fi hotspots to provide ubiquitous coverage to rival that of the cellular network. Whether used directly or as backhaul for Wi-Fi, WiMAX fills the gaps in the hotspot system, and possibly enables it to challenge the cellular network as it cannot realistically do right now. In the end, the technologies will coexist in a creative way, with WiMAX increasingly the dominant partner, and the non-standard alternatives will fade into the background.
On one hand we have WiMAX, on the other, 802.20, nicknamed ‘Mobile-Fi’, the first standard to be specifically designed from the outset
EXPANDING COMPETITION: WiMAX
to carry native IP traffic for fully mobile broadband access. According to the latest Revision 13 requirements specification, 802.20 is a ‘specification of physical and medium-access-control layers of an air interface for interoperable mobile broadband wireless access systems, operating in licensed bands below 3.5 GHz, optimized for IP data transport, with peak data rates per user in excess of 1 Mbps over distances of about 15 km. It supports various vehicular mobility classes up to 250 km/h in a MAN environment and targets spectral efficiencies, sustained user data rates, and numbers of active users that are all significantly higher than achieved by existing mobile systems.
This makes it lower powered than WiMAX but more intrinsically mobile, offering latency of 10 ms even in a fast moving vehicle, compared with 500 ms for 3G. Although the outcome of this battle is uncertain, delivery systems are sure to evolve that extend network access far beyond the limitations of Ethernet’s original wired model.
However, 802.20 has three critical weaknesses - WiMAX is starting to take on some of its remit; WiMAX has stronger and more aggressive support from key vendors; and the mobile operators, while relatively friendly towards 802.16, are hostile to 802.20.